Crop damage due to disease is a significant cause of yield reduction, and as a countermeasure, crop protection is widely performed with agricultural chemicals such as fungicides and disease damage resistant varieties used in combination. However, there arises a serious problem that use of fungicides induces pathogenic microbes of plant diseases to have resistance against the fungicides. Although methods of using a plurality of fungicides having different mode of action in combination have been widely employed to solve the aforementioned problem, influences on the environment are concerned in the current strategy mainly based on the use of fungicides. Therefore, development of a novel method for controlling disease damage with consideration for the environment has been desired.
Under the circumstances as described above, plant activators which activate endogenous defense systems of plants to control disease damage of the plants (also called as plant vitalizers or disease damage resistance inducers) have been focused. The plant activators have no problem of inducing resistance in pathogenic microbes of plant diseases, and have less direct influences on the ecosystem itself, and therefore they are expected to be crop protection means that can significantly reduce the stress on the environment.
When plants perceive invasion of pathogenic microbes, they operate a defense mechanism called hypersensitive cell death, which induces spontaneous death of cells surrounding an infection site to form characteristic necrotic lesions and thereby prevent spread of infection. Although it is expected that elucidation of the process of establishing the hypersensitive cell death leads to understanding of an activation mechanism of disease damage resistance response in plants, the details thereof have not yet been elucidated.
The acyl transferase (OsAT1) gene has recently been identified as a gene involved in biosynthesis of substances in rice plant (Plant Mol. Biol., 63, pp. 847-860, 2007), and it has been reported that, in an OsAT1 high expression strain, expression induction of acquired systemic resistance marker genes PBZ1 and PR1, accumulation of rice plant phytoalexins, and resistance to rice blast are improved (The 33rd Convention of the Pesticide Science Society of Japan, Matsuda et al., Subject number: C312, Apr. 1, 2008). Under assumption that a product resulting from a reaction catalyzed by OsAT1 might trigger the induction of a series of disease damage resistance responses, Matsuda et al. found six components, of which contents always increased when OsAT1 was overexpressed, and reported that one (UK1) of the compounds was estimated to be an amide compound formed by an amino-containing compound and hydroxylauric acid on the basis of MS/MS analysis. However, the chemical structure of this substance has not been fully identified.
Spermidine is one of typical polyamines and known to be involved in induction of cell death such as hypersensitive response (HR) through production of hydrogen peroxide (Plant Mol. Biol., 70(1-2), pp. 103-112, 2009; Plant Physiol., 132(4), pp. 1973-1981, 2003). Further, since reactive oxygen species such as hydrogen peroxide and nitrogen monoxide, which are important signals for HR, are also important signals for other disease damage resistance responses, they are considered to be possibly involved in disease damage resistance other than HR.
As for actions of spermidine derivatives on plants, it is so far known that 4N-hexanoylspermidine is accumulated in plant body of Pisum sativum with senility thereof (Plant Physiol., 10(4), 1177-1186, 1996). However, induction of resistance to plant diseases by spermidine derivatives has not been reported. Several cinnamic acid derivatives of spermidine are known, and a disease damage-inductive hydroxycinnamic acid derivative existing in Arabidopsis thaliana (The Plant Cell, 21, pp. 318-333, 2009), a hydroxycinnamic acid derivative having insecticidal activity or the like (Phytochemistry, 63, pp. 315-334, 2003), and polyamine derivatives (Nat. Prod. Rep., 22, pp. 647-658, 2005) have been reported. However, actions of these spermidine cinnamic acid derivatives for inducing resistance to disease damage of plants have not been reported.